We have described suppression of the mixed lymphocyte reaction in humans by thymus-derived T cells and soluble T cell derived factors. Such suppression is highly specific for HLA-D products on MLR responder lymphocytes. In the past year we have demonstrated that MLR suppressor cells are rare in healthy individuals but common in patients with Hodgkin's disease, a disorder characterized by diminished cell mediated immunity. Surprisingly, MLR suppressor cell activity is increased following treatment with lymphoid irradiation. In addition, we have discovered that the autologous mixed lymphocyte reaction is markedly diminished in virtually all patients with Hodgkin's disease, a finding which is even more dramatic than the presence of suppressor cells. In the past year we have succeeded in producing a monoclonal xenoantibody to a human T cell subset, but MLR suppressor T cells are not included in this subset. The goals for the coming year included: 1. extended studies of the possible role, in vivo, of suppressor T cells of the MLR and their possible induction by lymphoid irradiation; 2. analysis of the profound effect of autologous MLR in Hodgkin's disease; 3. continued production of monoclonal antibodies specific for human T cell subsets, including antibodies specific for MLR suppressor T cells; 4. further definition of the genetic restriction between suppressor cells and their target responder cells; 5. attempted growth of T cell clones with specific functions, including MLR suppression; and 6. initiation of biochemical analysis of suppressor T cell factors.